1. Field of the Invention
This invention relates to an air compressor, primarily for use in a vehicle air-actuated braking system, of the type having at least one compressor element operable by drive means to effect compression of air within a space, the compressed air usually being fed, in use, to a reservoir and thence on demand to the braking system for actuation of the latter.
2. Description of the Prior Art
In FIG. 1 of our co-pending British Patent Application No. 8215732 there is described an air compressor in which a compressor element is operable by drive means to effect compression of air within a space, the arrangement including a clutch for transmitting drive from the drive means to the compressor element when compression is required, the clutch being normally held in engagement by a spring device and being disengagable by a device responsive to a pressure resulting from the compressor output to interrupt the drive to the compressor element when said pressure reaches a predetermined value.
With such an arrangement, it is desirable to re-engage the clutch gradually after disengagement thereof in order to minimize shock loading of the compressor components. In our aforesaid British Application, it is proposed to use an unloader valve to hold open an inlet valve of the compressor temporarily in order to prevent compression during at least the initial stage of clutch re-engagement. However, this can be unduly complicated in practice and, in some circumstances, not entirely satisfactory in operation.